Turn url to clickable links © symfony 1.4

function.php

<?php

if (!defined('SF_AUTO_LINK_RE'))
{
  define('SF_AUTO_LINK_RE', '~
    (                       # leading text
      <\w+.*?>|             #   leading HTML tag, or
      [^=!:\'"/]|           #   leading punctuation, or
      ^                     #   beginning of line
    )
    (
      (?:https?://)|        # protocol spec, or
      (?:www\.)             # www.*
    )
    (
      [-\w]+                   # subdomain or domain
      (?:\.[-\w]+)*            # remaining subdomains or domain
      (?::\d+)?                # port
      (?:/(?:(?:[\~\w\+%-]|(?:[,.;:][^\s$]))+)?)* # path
      (?:\?[\w\+%&=.;-]+)?     # query string
      (?:\#[\w\-/\?!=]*)?        # trailing anchor
    )
    ([[:punct:]]|\s|<|$)    # trailing text
   ~x');
}

/**
 * Turns all urls into clickable links.
 */
function _auto_link_urls($text, $href_options = array(), $truncate = false, $truncate_len = 40, $pad = '...')
{
  $href_options = _tag_options($href_options);

  $callback_function = '
    if (preg_match("/<a\s/i", $matches[1]))
    {
      return $matches[0];
    }
    ';

  if ($truncate)
  {
    $callback_function .= '
      else if (strlen($matches[2].$matches[3]) > '.$truncate_len.')
      {
        return $matches[1].\'<a href="\'.($matches[2] == "www." ? "http://www." : $matches[2]).$matches[3].\'"'.$href_options.'>\'.substr($matches[2].$matches[3], 0, '.$truncate_len.').\''.$pad.'</a>\'.$matches[4];
      }
      ';
  }

  $callback_function .= '
    else
    {
      return $matches[1].\'<a href="\'.($matches[2] == "www." ? "http://www." : $matches[2]).$matches[3].\'"'.$href_options.'>\'.$matches[2].$matches[3].\'</a>\'.$matches[4];
    }
    ';

  return preg_replace_callback(
    SF_AUTO_LINK_RE,
    create_function('$matches', $callback_function),
    $text
    );
}